Question: Suppose the diameter of a circle is ${2}$. What is its area?
Explanation: ${d = 2}$ ${K = 1\pi}$ First, find the radius: $r = d/2 = {2}/2 = {1}$ Now find the area: $K = \pi r^2$, so $K = \pi \cdot {1}^2 = {1\pi}$.